The 430exII will work fine with the 580exII but you'll have a shorter max. range vs. a pair of 580exII. The extra .8 stop of power the 580exII offers helps when using modifers, bouncing and HSS outdoors. Also consider that with lighting ratios other than A:B=1:1 the off camera 430exII will be working 2-8x more than the 580exII Master.

SInce flash is the cheapest part of the gear (compared to camera and lenses) and will last a long time if not abused the extra money spend on the 580ex is actually, I think, a good value in the long run which is why I bought a pair of 580ex.

I'd also suggest trying the built-in signaling before buying radio triggers. I've been triggering mine optically without any problems from upto 50', through doorways, etc. You can always buy the triggers later when you find you actually need them.

The 430 is intended to "become" the third flash, I was trying to figure a way of saving a couple hundred bucks around Christmas time, so I can spoil my kids a little more. I hate spending money on myself. lol

That is the plan though. 2 580s, 1 430, and probably a couple of Einsteins eventually.